| Dimethyl disulfide（DMDS）is effective in controlling destructive soilborne diseases without causing ozone holes,which makes them become one of the most promising alternatives to Methyl bromide.The volatilization of DMDS is very strong,and it can be rapidly volatilized into gas to spread around in the soil,which can kill harmful organisms in the soil,including soil-borne pathogens,nematodes,underground pests,weeds.DMDS is used in the field with stock solution that pollutes the environment,strong pungent odor,and the high risk of human exposure.Therefore,it is very important to develop DMDS controlled release formulation.In this paper,the preparation method of cyclodextrin（CD）encapsulated DMDS controlled release formulation was established and successfully prepared.At the same time,the characterization of DMDS controlled release formulation,controlled release effect,use safety,biological activity,storage stability and release mechanism were evaluated.The main results of the study are showed as follows:1.The preparation method of cyclodextrin encapsulated DMDS controlled release formulation（DMDS@HP-β-CD）was established.Using 2-hydroxypropyl-β-cyclodextrin（HP-β-CD）as carrier,the controlled release formulation of soil fumigant DMDS was prepared by stirring method.DMDS@HP-β-CD was prepared at different temperatures（25℃,30℃,35℃）,stirring time（1h,2 h,3h）,and mass ratios of HP-β-CD and DMDS（1:1,1:2,2:1）.Orthogonal experimental design was used to explore the best preparation scheme.Under the stirring conditions of temperature（25℃）,time（1h）,mass ratio（1:1）and string speed（200 r/min）,the prepared DMDS@HP-β-CD was washed by ethyl acetate for 3 times,and the loading content and encapsulation efficiency were determined to be 9.52%and 81.49%.2.Characterization of DMDS@HP-β-CD.The prepared samples were characterized by FT-IR,TGA and SEM.The results showed that the DMDS molecules were encapsulated into the HP-β-CD cavity and appearance changed.3.Determination of controlled release effect.The field usage of DMDS was 40 g a.i./m2（102.6mg/kg）and the release rate of DMDS was determined by simulating the air flow rate of 100 m L/min in the field at room temperature.The results showed that the release time of DMDS@HP-β-CD was twice as long as that of DMDS when the release rate was maintained at a high concentration（>5μg/min）.This proves that DMDS@HP-β-CD has the controlled release property.4.Release kinetics equation fitting.The release kinetics equation was fitted with the controlled release results,and the results showed that the release of DMDS in DMDS@HP-β-CD was in good agreement with the Peppas model,and the fitting model was Q=0.0909t0.6699.5.Evaluation of safety in use.Cucumber seeds were planted in soil fumigated at 28℃for 7 days and exposed for 1 day.The germination rate,root length and Germinal length of cucumber treated with DMDS and DMDS@HP-β-CD had no significant inhibitory effect compared with blank control.6.Biological activity evaluation.At the active ingredient concentrations of 102.6 mg/kg and205.2 mg/kg,the adjusted mortality rates of DMDS@HP-β-CD against Meloidogyne spp.was 90.25%and 97.66%,68.59%and 73.55%for Fusarium spp.,and 64.93%and 69.41%for Phytophthora spp.Under the same concentration of active ingredient,the control efficacy of DMDS against Meloidogyne spp.was 94.78%and 100%,77.68%and 82.64%for Fusarium spp.,and 69.41%and83.58%for Phytophthora spp.The control effect of DMDS@HP-β-CD was not significantly different from that of DMDS,except for the Phytophthora spp.at the active ingredient concentration of205.2mg/kg.7.Storage stability.0.02g DMDS@HP-β-CD was accurately weighed and stored in a 20 m L headspace flask and stored at different temperatures（4℃,15℃,25℃and 35℃）during opening and sealing.The measured residual quantities at 4℃for 10 days were 74.11%and 84.62%.8.Release mechanism.DMDS@HP-β-CD was applied in the soil at active ingredient concentration of 102.6 mg/kg,and the release rate was monitored on the surface.The results showed that the release rate of DMDS stock solution decreased to 5 ug/min at 3h,while,it took 6 h for DMDS@HP-β-CD to decrease to the same release rate.The accumulating release percentage of DMDS was 36.25%and DMDS@HP-β-CD was 36.70%.The half-life period of DMDS@HP-β-CD in soil is 1.5 times that of the active ingredient of DMDS.The above study results showed that the effect of HP-β-CD encapsulation of soil fumigant DMDS and some aspects of evaluation were good.In addition,this study provided an important theoretical reference for the development and application of soil fumigant DMDS controlled release formulation.At the same time,it can not only reduce the strong pungent smell of DMDS stock solution when it was used,reduce human exposure,but also reduce the using dosage,decrease environmental pressure and production cost,which plays an important role in the control of soil-borne diseases,the planting of cash crops and the sustainable development of agriculture. |
